Such a valve-gated injection moulding device is known from EP-A-282 999. In the known injection moulding device, a mechanically actuated valve pin is used for opening and closing the gate in a so-called hot-runner injection moulding device. In the hot-runner device, heating elements are provided along the melt passage of the nozzle for maintaining the thermoplastic material which is to be injected through the gate into an injection cavity, in a molten state. The valve pin is guided in a guide bushing which also functions as a seal for the thermoplastic material. Therefore there is very little play between the valve pin and the guide bushing such as to maintain a sufficient seal (for instance at a 4 millimeter diameter of the valve pin, only 0.005 millimeter play can be allowed). The valve pin should be very accurately guided to avoid jamming of the valve pin. Thereto it is very important to only load the valve pin in an axial direction and to avoid exerting radial forces thereon. Radial forces exerted on the valve pin cause a friction which should be overcome, requiring more energy in the actuating means for the valve pin, may cause stick-slip phenomena, inaccurate positioning of the valve pin, wear, etc. As the guide bushing of the valve pin cannot be lubricated, the avoidance of radial forces is very important. During the high operating temperatures (200-300.degree. C.) most lubricants will flow out of the lubrication gap, and can leak into the molten thermoplastic material causing contamination.
In the known actuating device of the valve pin as shown in EP-A-0 282 999, the rearward end of the valve pin is cylindrical and is received into a U-shaped bracket of a lever which radially extends towards the valve pin. By pivoting the lever around a pivot point, the valve pin can be moved in the axial direction, while the cylindrical surface of the valve pin head slides with respect to the actuating surfaces of the U-shaped bracket at the end of the lever. The known actuating device has as a disadvantage that radial forces are still exerted on the valve pin head. Accurate guiding of the rearward end of the valve pin is not possible. Furthermore, the stroke of the valve pin is limited and cannot be easily adjusted to prevailing process conditions after mounting the nozzle in the cavity plate.
It is also known to provide actuating devices which are axially aligned with the valve pin. These systems have as a disadvantage that adjustment of the valve pin height after mounting in the cavity plate is no longer possible. Furthermore is a large space above the nozzle required for such axially aligned systems. For single-nozzle systems which are directly connected to the injection moulding device, this space is not available.